Long ā is substituted for the final of deva and sumna before the Denominative kyac in yajuṣa kāṭhaka,
As देवायन्तो यजमानाः सुम्नायन्तो हवामहे ॥ Why in the Yajus? Observe देवाञ्जिगाय सुम्नयुः ॥ Why do we say in the Kathaka? Observe सुम्नयुरिदमासात् ॥,